Your parents have a low level of trust for some reason. A natural reaction would be to become defensive and angry but rather than do that; it's more productive to go into problem-solving mode. It would be beneficial if you can work to get to the bottom of WHY they feel the way they do. For example:
1) Is there someone in the family who experienced a teenage pregnancy and they fear your fate will be the same?
2) Are you an only or first child and they feel confused about how to handle your emerging independence?
3) Have you made some poor choices in the past that cause them to question your judgment when it comes to boys?
4) Is there something about the boy that is particularly objectionable? Do they need to get to meet him or get to know him better?
5) Is there an alternative location where they would trust you and your crush to hang out together unattended after school for a couple of hours, such as the local mall, public library, or a favorite teen fast food restaurant? (Be ready to supply ideas.)
It would be helpful for you to have a calm discussion with them to find out what you can do to show them you're interested in companionship and hanging out with your crush outside of school rather than sex. Your challenge is to keep it calm and nonreactive.
Your objective should be to listen to their feelings and perspective and to explain yours. Communication and patience with them even though they seem unreasonable will get you through this.